Impact

A problem in the ECMAScript (JavaScript) specification of async generators, introduced by a May 2021 spec refactor, may lead to mis-implementation in a way that could present as a security vulnerability, such as type confusion, pointer dereference, and uncaught exception.

Details

The internal async generator machinery calls regular promise resolver functions on IteratorResult ({ done, value }) objects that it creates, assuming that the IteratorResult objects will not be then-ables. Unfortunately, these IteratorResult objects inherit from Object.prototype, so these IteratorResult objects can be made then-able, triggering arbitrary behaviour, including re-entering the async generator machinery in a way that violates some internal invariants.

Fix

The ECMAScript specification is a living standard and the issue has been addressed at the time of this advisory's public disclosure. JavaScript engine implementors should refer to the latest specification and update their implementations to comply with the AsyncGenerator section.

References

• 4cb5a69